1 #include <stdio.h>
  2 #include <stdlib.h>
  3 #include <dirent.h>
  4
  5 int main(int argc,char *argv[])
  6 {
  7     DIR *dp;
  8     struct dirent *dirp;
  9
 10     if(argc != 2)
 11         printf("err argument");
 12
 13     if((dp = opendir(argv[1])) == NULL)
 14         printf("can't open %s",argv[1]);
 15
 16     while((dirp = readdir(dp)) != NULL)
 17         printf("%s\n", dirp->d_name);
 18
 19     closedir(dp);
 20     exit(0);
 21 }

  1 #include "stdio.h"
  2 #include "apue.h"
  3 
  4 int main(void)
  5 {
  6     int c;
  7     while((c=getc(stdin))!=EOF)
  8         if(putc(c,stdout)==EOF)
  9             printf("output error");
 10 
 11     if(ferror(stdin))
 12         printf("input error");
 13 
 14     exit(0);
 15 }
~          

  1 #include "apue.h"
  2 int main(void)
  3 {
  4     printf("hello world from proces ID %d\n",getpid());
  5     exit(0);
  6 }